The single most important...
The single most important consideration in the building and running of a racing engine is durability. It won’t matter where you run in a given race if the engine fails before the checkered flag. To this point, Smokey frequently said he “never saw a broken engine win a race.”
I built my first high-performance engine in 1953, first racing engine in 1954, and first successful circle track engine in 1956. OK, that seriously dates me in the business of building a variety of engines. But along the way, I experienced some hard-learned lessons on what it takes to keep from wasting money, time, and losing races. And then I came into contact with someone far more experienced in the business of building winning race engines. He drilled into me three considerations that are critical and unavoidable: affordability, reliability, and the importance of spare parts. Were he alive today, he'd put just as much pressure on you as he did on me back then. You recall the name Smokey Yunick? Well, here's a condensation of what ol' Smoke had to say about the three categories just listed.
His first bone of contention was that many engine builders don't know what they have available to spend before building their engine of choice. In his view, engine builders often assemble a group of parts that they figure will fit together in a way that wins races, seldom considering the fundamental need to integrate their functions. He maintained that it does no good to spend hard-earned money on "trick parts" that won't take the place of sound engine planning and parts integration. It all costs money, including the mistakes, so begin with some sort of a budget.
Also within the category of "affordability," he frequently advised that there's basically relatively inexpensive racing and very expensive racing, with "damned little" in between. Of course, just about all racing is expensive (depending upon your frame of reference), but he was making a distinction between one and the other as each pertains to power levels.
For example, let's assume you've been reasonably successful racing an engine at a relatively low power level, possibly below 500 hp, and have found (either through study or experience) a combination that works pretty well and has acceptable affordability. Then, at some point, you decide to raise the power level of this basic combination of parts. Smokey's perspective was that such a move typically involves better and (highly likely) more expensive parts, so choices should be made very wisely. Seek every possible source of information in your decision-making effort. It's reasonable to assume parts manufacturers are a good source of information but consult with experienced engine builders, if you have the opportunity. Process as much information as possible before drawing conclusions.
An example he used was that maybe a "bigger" set of cylinder heads would open up a higher range of rpm. By themselves, in the original parts package, there's a chance you'd not see a power gain commensurate with the cost of the heads. So now you're faced with the installation of a camshaft capable of higher engine speed, intended to match the increased flow capability of the heads. The next event, he reckoned, is that higher rpm and failure to improve the engine's lower-end structure and oiling could result in "driving over the crank" on the first trip down the backstretch.
His point was that substantial changes in power level (working basically in one area of an engine at a time), especially because you've inadvertently spent more money in the process, are difficult if not impossible to make without impairing an engine's durability. As a consequence, he advocated stepping back and taking an overall look at a complete parts package and its ability to withstand the pressures of higher horsepower, rpm or both. Parts functionality is best accomplished by matching all parts to address the intended level of power, not just components as cylinder heads and camshafts, as a for instance.
His second area of concern deals with component and assembled engine durability. He maintained that the single most important consideration in the building and running of a racing engine is durability. It won't matter where you run in a given race if the engine fails before the checkered flag. To this point, Smokey frequently said he "never saw a broken engine win a race." His overriding philosophy was that durability is far more important than speed on the track, and any engine modification that jeopardizes durability is a total waste of time and money.
And then there was the matter of what he called the "crossbreeding of techniques," involving different forms of racing. As an example, he compared a drag race engine to one built for endurance racing and while the differences between these two venues are obvious, his focus was primarily on the weight differences between the components used. His observation, for the most point, was that money is often wasted on lightweight parts that ultimately lack the durability of slightly heavier ones that will last in an endurance race. Further, he noted that whatever choices an engine builder makes that compromise strength can affect durability; choices that will sooner than later prove to be the wrong ones.
Finally, there is the issue of spare parts. After watching how Smokey so often configured his engine packages, I prefer to use the term "parts interchangeability" rather than spare parts. Here's why. Unless the availability of funds is not a problem, especially once a given engine combination has proven to be competitive and reliable, building spare engines that represent significant departures from such a combination can be costly. Especially when you experience an engine failure, certain parts can often be reused, certainly among the weekly racer community. If you've collected or built back-up parts or engines that bear little in common with each other, the degree of interchangeability is diminished.
Work on fine-tuning an engine combination that makes competitive power and doesn't break. Smokey's concern about the avoidance of "trick parts" would turn up in virtually any response he provided on building a reliable engine that was competitive. For example, tuning on the intake and exhaust system can produce changes in torque vs. engine speed are generally not expensive (compared to major internal engine components) and will produce fewer chances for parts failures than the risks (and expense) encountered with lightweight pistons or rotating assemblies, as an example.
Smokey often urged engine builders (and racers) to ignore the "trick" pieces and combinations, use the best parts you can afford, and do what you can to make components interchangeable for when you are rebuilding an engine. In both the short- and long-runs, it'll save you money on engine parts and leave money for things like fuel and tires.
In the final analysis, the cost of racing, certainly with respect to engines, should not be an ongoing issue with the weekly racer. Build something upon which you can rely, week to week and race to race. If you can accomplish this and will spend some quality time reading and applying the exceptionally-good information Bob Bolles shares about suspension fundamentals and the art of chassis tuning (on a monthly basis), chances are some of Smokey's experience about being able to finish the races you start (in terms of engine power and life) will culminate in more affordable and enjoyable racing, while improving your chances of winning. You think?